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Do taped seams need to be foamed

Smokey059 | Posted in General Questions on

I’m getting ready to put  blow in cellulose into the attic and while getting wires and conduit etc thru,  I turned off the lights in the attic and noticed I could see light thru the seams of the plywood ceiling I installed. The plywood seams were all taped with  3m  3″ tape. My question is do these seams in the attic need to be foamed also or is the tape sufficient to keep the air seal intact.

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  1. Matt F | | #1

    The tape will let a bit of light through, but not air.

    If you really want know the answer, have a blower door test done.

    Or what I do, is use a few box fans in the windows and an IR camera.

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi Smokey059.

    Many builders are using just tape on plywood and OSB for rigid air barriers on the ceiling, without foam. But I agree with Matt. Do all of your air sealing and have a blower door test done before covering anything up that may still need some attention. You can find some info on the air sealing and testing process in this article: The Four Control Layers of a Wall.

  3. Smokey059 | | #3

    Thanks for the replies. Ill just hit them with the foam gun as added protection. A another hour or two after the many spent already wont matter much.

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